There have been various types of analog-to-digital converters (ADC), one of them utilizes a sigma-delta modulator. A sigma-delta modulator includes a quantizer that converts analog signals into digital signals. Not only single-bit but also multibit quantizer has been used for sigma-delta modulators. The use of multibit quantizer can mitigate the problem of instability especially for a single-loop sigma-delta modulator and can help to improve a signal-to-noise ratio (SNR) or signal-to-noise and distortion ratio (SNDR). A major drawback associated with the use of a multibit quantizer in a sigma-delta modulator is non-linearity, which is caused when the output signal from the quantizer is converted to an analog signal by a digital-to-analog converter (DAC) on the feedback loop.